Printed circuit board assemblies are used in computers, communications equipment, televisions and many other products. In a typical printed circuit board assembly, many electrical components are attached to the top and bottom surfaces of a printed circuit board (PCB). Since the electronics manufacturing industry is highly competitive, it is important to maximize the through-put and accuracy of attaching components to the PCBs.
Many PCB assemblies are manufactured by surface mounting components to the PCBs. For example, many Single In-line Memory Modules and Dual In-line Memory Modules have a plurality of memory dies or packaged memory devices surface mounted to a PCB. To surface mount components to one side of a PCB, a dispenser deposits solder pads and/or adhesive pads onto the PCB, and then a component placing machine presses the components against the solder and adhesive pads. After one side of the PCB has been populated with components, the PCB may be inverted and the process may be repeated to surface mount components to the other side of the PCB. The solder/adhesive dispensers are typically pen-type dispensers or stenciling machines, and the component placing machines are typically turret-type pick-and-place devices. After the components are mounted to the PCB, the populated PCB passes through a reflow oven to melt the solder paste and thus solder the components to the PCB.
Surface mounting components to PCBs raises several manufacturing issues that are best understood in light of conventional component placing machines or pen-type glue dispensers. Conventional component placing machines generally have a programmable component mounting head with a mechanism that places selected components at desired locations on a PCB. Conventional component placing machines may also have a PCB holder with edge clamps that engage the edges of a PCB, an elevator table under the PCB holder, and two spaced-apart conveyor tracks to transport the PCB along a conveyor line. In operation, the conveyor tracks transport the PCB until it is positioned at the PCB holder, and then the clamps engage the edges of the PCB. Once the PCB is securely held by the clamps, the mounting head places components at desired locations on the PCB.
To enhance the through-put of finished PCB assemblies, surface mounting processes must quickly and accurately attach large numbers of very small and/or complex components to the PCBs. The dispensing machines, for example, must accurately deposit very small solder pads and adhesive pads at precise locations on the PCB. Similarly, the component placing machines must accurately press the electrical components onto the pads at precise locations so that the electrical terminals of the components engage the desired solder pads. For proper placement of solder paste, adhesives and components onto a PCB, the PCB must remain flat as the dispensing and component placing machines exert forces against the PCB. Thus, it is desirable to support the underside of the PCB during processing to inhibit bowing, deflection or warping of the PCB.
To support the underside of PCBs, a plurality of single-pin board supports are attached to the elevator table of a processing machine to engage interior areas on the underside of a PCB assembly. Single-pin board supports typically have a bracket slidably attached to the elevator table and a pin threadedly engaged with a hole in the bracket. The pin is laterally positioned under a PCB by sliding the bracket across the elevator table, and the pin is vertically positioned by rotating it with respect to the bracket. Several types of PCB assemblies require twenty or more single-pin supports to adequately support the PCBs.
Conventional single-pin board supports, however, encounter several manufacturing issues when several small lots of different PCB assemblies are manufactured in a short period of time. Different PCB assemblies typically have different PCBs with different dimensions. The height and location of each single-pin support, therefore, must be adjusted each time a different lot of PCB assemblies is manufactured. However, it is extremely time-consuming to accurately adjust such a large number of pins to be at the desired height and location. Moreover, with some PCBs, there is not adequate space to install enough single-pin supports to properly support the PCB. Thus the set-up time to configure conventional PCB supports and the lack of flexibility in positioning such supports may significantly increase the cost of manufacturing small lots of PCB assemblies.